Ischemic tissue damage needs angiogenesis in the damaged area for the tissue recovery. After birth, new vessels are generated by angiogenesis, arteriogenesis, and vasculogenesis. Angiogenesis is related to the proliferation and migration of endothelial cells that are developed from the mature endothelial cells, while arteriogenesis is the process of remodeling of arteriolar connection as collateral vessels (Carmeliet, P. (2000) Mechanisms of angiogenesis and arteriogenesis. Nat. Med. 6, 389.395). In the meantime, vasculogenesis is progressed through the course wherein endothelial progenitor cells (EPC) are developed into the mature endothelial cells (Asahara, T. and Kawamoto, A. (2004) Endothelial progenitor cells for postnatal vasculogenesis. Am. J. Physiol. Cell Physiol. 287, 572.579.). EPCs that are developed from the bone marrow and circulated thereafter to migrate to the area of injury of blood vessels and are involved in angiogenesis by being inserted directly in the newly generated blood vessels or by inducing the secretion of various angiogenesis factors and nutritional factors (Jujo, K., Ii, M. and Losordo, D. W. (2008) Endothelial progenitor cells in neovascularization of infracted myocardium. J. Mol. Cell. Cardiol. 45, 530.544., Urbich, C., Aicher, A., Heeschen, C., Dernbach, E., Hofmann, W. K., Zeiher, A. M. and Dimmeler, S. (2005) Soluble factors released by endothelial progenitor cells promote migration of endothelial cells and cardiac resident progenitor cells. J. Mol. Cell. Cardiol. 39, 733.742.). Therefore, EPCs are the potential target of concern for the treatment by revascularization (Jujo, K., Ii, M. and Losordo, D. W. (2008) Endothelial progenitor cells in neovascularization of infracted myocardium. J. Mol. Cell. Cardiol. 45, 530.544.).
Recent studies on EPCs are mainly focused on the EPCs that are genetically modified ex vivo in order to increase the functions of cells. For that purpose, vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1a have been used because they displayed the activity of increasing the pro-angiogenic capacity of EPCs (Iwaguro, H., Yamaguchi, J., Kalka, C., Murasawa, S., Masuda, H., Hayashi, S., Silver, M., Li, T., Isner, J. M. and Asahara, T. (2002) Endothelial progenitor cell vascular endothelial growth factor gene transfer for vascular regeneration. Circulation 105, 732.738., Jiang, M., Wang, B., Wang, C., He, B., Fan, H., Guo, T. B., Shao, Q., Gao, L. and Liu, Y. (2008) Angiogenesis by transplantation of HIF-1a modified EPCs into ischemic limbs. J. Cell. Biochem. 103, 321.334.).
Haptoglobin (Hp) is an acute-phase glycoprotein existing in blood circulation system, and the well known biological function of Hp is capturing hemoglobin. Hp forms HP-hemoglobin complex which is known to be functioning to prevent hemoglobin-stimulated oxidative tissue damage (Lim, Y. K., Jenner, A., Ali, A. B., Wang, Y., Hsu, S. I., Chong, S. M., Baumman, H., Halliwell, B. and Lim, S. K. (2000) Haptoglobin reduces renal oxidative DNA and tissue damage during phenylhydrazine-induced hemolysis. Kidney Int. 58, 1033.1044., Buehler, P. W., Abraham, B., Vallelian, F., Linnemayr, C., Pereira, C. P., Cipollo, J. F., Jia, Y., Mikolajczyk, M., Boretti, F. S., Schoedon, G., Alayash, A. I. and Schaer, D. J. (2009) Haptoglobin preserves the CD163 hemoglobin scavenger pathway by shielding hemoglobin from peroxidative modification. Blood 113, 2578.2586).
Hp can be expressed in artery (Smeets, M. B., Pasterkamp, G., Lim, S. K., Velema, E., van Middelaar, B. and de Kleijn, D. P. V. (2002) Nitric oxide synthesis is involved in arterial haptoglobin expression after sustained flow changes. FEBS Lett. 529, 221.224.) and thus can be functioning as a cell migration factor that is particularly involved in arterial restructuring (de Kleijn, D. P. V., Smeets, M. B., Kemmeren, P. P. C. W., Lim, S. K., van Middelaar, B. J., Velema, E., Schoneveld, A., Pasterkamp, G. and Borst, C. (2002) Acutephase protein haptoglobin is a cell migration factor involved in arterial restructuring. FASEB J. 16, 1123.1125., Lohr, N. L., Warltier, D. C., Chilian, W. M. and Weihrauch, D. (2005) Haptoglobin expression and activity during coronary collateralization. Am. J. Physiol. Heart Circ. Physiol. 288, H1389.H1395).
However, there are no reports so far that suggest the mutant haptoglobin can induce angiogenesis.
Therefore, the present inventors studied and confirmed that the mutant haptoglobin had the higher activity of promoting angiogenesis than that of the wild type haptoglobin, leading to the completion of this invention.